Packaged RF power devices typically include a transistor die mounted on a base and enclosed in a package. An RF input signal is supplied to the transistor through an RF input lead that extends from outside the package to the inside of the package, and an RF output signal is delivered from the device through an RF output lead that extends from inside the package to the outside. An input matching circuit can be included within the package, and can be connected between the RF input lead and an input terminal of the RF transistor. The input matching circuit provides an impedance match at the input of the transistor at the fundamental operating frequency of the transistor.
The RF transistor can include a large periphery transistor die that includes a number of discrete transistor cells on a common substrate and connected in parallel. Input matching can be particularly beneficial for such devices, as it can increase the usable bandwidth of the devices. However, the input matching network typically includes a single capacitor, which can create a lower frequency feedback path between adjacent cells of the large periphery transistor die. This feedback path can reduce the stability of the overall device.
Furthermore, the impedance values of elements of the input matching network must be carefully selected to avoid creating odd mode oscillations. Selection of the impedance values, including selection of appropriate inductances through bond wire lengths, can limit the topology of the matching network.